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DEFECT STRUCTURE OF DIAMOND FILM AT THE INTERFACE WITH AMORPHOUS CARBON Li CHANG Materials Research Laboratories, Industrial Technology Research Institute, Chutung, Hsinchu 31015, Taiwan, R.O.C. ABSTRACT Diamond films prepared by microwave plasma chemical vapor deposition, using a gas mixture of methane and hydrogen with ethanol, were formed on silicon substrates. Highresolution transmission electron microscopy was employed to characterize the microstructure at interface regions. It was found that the diamond crystals were grown on an amorphous carbon layer. Twins and stacking faults were observed at the regions interfaced with the amorphous carbon layer, suggesting that the defects may already exist in the nucleation stage and at the very first stage of growth. Also, some diamond nuclei embedded in the amorphous layer were observed. INTRODUCTION Diamond films can now be prepared at low temperatures below 1000 °C by various chemical vapor deposition (CVD) methods using gas mixtures of carbon-containing gases with hydrogen at a pressure from 10 mbar to atmosphere [1-4]. Though CVD diamond films have many excellent properties, practical applications require good adhesion with substrates. Thus, the adhesion may be dependent on the characteristics of the interface between the diamond film and the substrate. Another concern about the interface is that hetero-epitaxial growth of diamond films on non-diamond materials has not been successful, which is strongly dependent on the interface. Also, the quality of diamond films may be affected by the interface structure at the early stage of growth. Transmission electron microscopy (TEM) is a well-established technique for the characterization of the interface because of its imaging capabilities for high resolution and structural determination. However, cross-section TEM specimen preparations for diamond films with substrates expose difficulty due to the large difference in ion milling rate between diamond and substrates, which would lead to only the diamond film left without the substrate at the end of ion milling. Though some researchers have used cross-sectional TEM to perform interface characterization [5-10], it is still inadequate to understand the nucleation and growth phenomena at the initial stage. The present work illustrates TEM observation of the interface between a diamond film and an amorphous layer grown on a silicon substrate by microwave CVD. EXPERIMENTAL Diamond films were grown by microwave plasma CVD using a gas mixture consisting of methane and hydrogen with ethanol. Silicon wafers (3 mm x 1 mm x 0.5 mm) were used as the substrates. Before deposition, the wafers were ultrasonically polished in a methanol bath with diamond powders of I #m. Then, the surface received the hydrogen plasma at 800 °C immediately before deposition to clean the surface. The substrate temperature estimated by an optical pyrometer was about 850 *C. The cross-sectional TEM specimens were prepared as follows: epoxy was used to glue Si substrates with diamond films in face-to-face orien